Some Mac OS 9 control panels configure system components that are already configured by System Preferences in Mac OS X. When Mac OS X detects a redundant control panel during Classic startup, it does not load the control panel. However, redundant control panels are still visible in Classic when you choose Apple > Control Panels. If you try to use the Mac OS 9 version of a redundant control panel, you will see an alert prompting you to perform the task in Mac OS X System Preferences instead. You should also be aware that third-party control panels and extensions might not work properly in Classic. Contact the third-party vendor to ensure compatibility.
MORE INFO
Refer to Knowledge Base document 107135, "Mac OS X 10.2: About Using Mac OS 9 Control Panels in the Classic Environment."
The following Mac OS 9 control panels are not used in Classic (Classic will use the settings you assign in Mac OS X System Preferences instead):
AppleTalk
Control Strip
Date & Time
Energy Saver
File Exchange
Infrared
Location Manager
Memory
Modem
Mouse
Multiple Users
Password Security
PowerBook SCSI Disk Mode
Remote Access
Startup Disk
TCP/IP
Trackpad
Web Sharing